U.S. patent number 8,239,091 [Application Number 12/671,116] was granted by the patent office on 2012-08-07 for method for detecting a "rotating stall" fault in a compressor fed by an inverter.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Axel Mertens, Gerhard Neeser.
United States Patent |
8,239,091 |
Mertens , et al. |
August 7, 2012 |
Method for detecting a "rotating stall" fault in a compressor fed
by an inverter
Abstract
The invention relates to a method for detecting a rotating stall
fault in a compressor (12) which is driven by means of a
three-phase current motor (8) fed by an inverter. According to the
invention, an instantaneous estimated value (^m) which is
calculated from measured power converter output currents (iS1, iS2,
iS3) and a measured rotational-speed-proportional signal (.omega.)
is compared with an instantaneous setpoint value (m*) determined
from a measured rotational-speed-proportional signal (.omega.) and
a predetermined rotational-speed-proportional signal (.omega.*), in
such a way that in the case of inequality a signal (SRS) is
generated which indicates that the rotating stall fault has
occurred. In this way, it is possible for the rotating stall fault
to be detected without pressure sensors and/or oscillation pickups
in a compressor (12) which is driven with a three-phase current
motor (8) fed by inverter.
Inventors: |
Mertens; Axel (Wedemark,
DE), Neeser; Gerhard (Neunkirchen, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Munchen, DE)
|
Family
ID: |
39884155 |
Appl.
No.: |
12/671,116 |
Filed: |
July 28, 2008 |
PCT
Filed: |
July 28, 2008 |
PCT No.: |
PCT/EP2008/059853 |
371(c)(1),(2),(4) Date: |
January 28, 2010 |
PCT
Pub. No.: |
WO2009/016145 |
PCT
Pub. Date: |
February 05, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100198480 A1 |
Aug 5, 2010 |
|
Foreign Application Priority Data
|
|
|
|
|
Jul 30, 2007 [DE] |
|
|
10 2007 035 712 |
|
Current U.S.
Class: |
701/31.7;
415/118; 701/100 |
Current CPC
Class: |
F04D
27/0292 (20130101); F04D 27/0261 (20130101); F04D
25/06 (20130101); F04D 27/001 (20130101); Y02B
30/70 (20130101); F05D 2270/335 (20130101) |
Current International
Class: |
G06F
19/00 (20060101) |
Field of
Search: |
;701/29.1,31.7,32.8,100
;415/17,27,118 ;340/966 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
JM. Sorokes; Rotating Stall--An Overview of Dresser-Rand
Experience; [Online] Dresser-Rand, Olean, NY, USA; Magazine; US (=
2007Q13156), Feb. 19, 2003, pp. 1-22, XP007906222-. cited by
other.
|
Primary Examiner: Camby; Richard M.
Attorney, Agent or Firm: Feiereisen; Henry M. Day; Ursula
B.
Claims
What is claimed is:
1. A method for detecting a "rotating stall" fault in a compressor
driven by a converter-fed three-phase motor, comprising the steps
of: measuring converter output currents and a signal proportional
to a motor speed; calculating from the measured converter output
currents and the measured speed-proportional signal an estimated
torque value; computing a torque value difference between the
estimated torque value and a nominal torque value determined from
the measured speed-proportional signal and a predetermined
speed-proportional signal; and if the computed torque value
difference is greater than an operating-point-dependent stationary
value, generating a fault signal which indicates that a "rotating
stall" fault has occurred.
2. The method of claim 1, further comprising the step of
differentiating the calculated estimated torque value.
3. The method of claim 1, further comprising the step of
differentiating the determined nominal torque value.
4. The method of claim 1, wherein the operating-point-dependent
stationary value is set to zero.
5. The method of claim 1, wherein the estimated torque value and
the nominal torque value are filtered.
6. The method of claim 1, wherein the torque value difference is
filtered.
7. The method of claim 1, wherein the fault signal generates an
alarm signal.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is the U.S. National Stage of International
Application No. PCT/EP2008/059853, filed Jul. 28, 2008, which
designated the U.S. and has been published as International
Publication No. WO 2009/016145 and which claims the priority of
German Patent Application, Ser. No. 10 2007 035 712.7, filed Jul.
30, 2007, pursuant to 35 U.S.C. 119(a)-(d).
BACKGROUND OF THE INVENTION
The invention relates to a method for detecting a "rotating stall"
fault in a compressor which is driven by a converter-fed
three-phase AC motor.
The following faults can occur when operating compressors, namely
"surge", "stall" and "rotating stall" faults. In the publication
with the title "Rotating Stall --An Overview of
Dresser-Rand-Experience" by J. M. Sorokes, published February 2003
by the Dresser-Rand Company, Houston, Tex., these faults are
briefly explained before discussing the "rotating stall" fault in
detail.
The "rotating stall" fault frequently precedes the "surge" fault.
Both faults are permissible to a limited extent, but because of the
vibrations which occur with the "rotating stall" fault, this gives
rise to material fatigue. This "rotating stall" fault has
previously only been detected in large compressors with the help of
pressure sensors and/or vibration recorders. The quality and the
selectivity of the detection depend on the positioning and the
number of sensors and/or recorders. These pressure sensors and/or
vibration recorders are laborious to install and evaluate. When
using pressure sensors, problems can occur relating to the sealing
of the installation points and relating to the selectivity of the
state detection.
A compressor which is driven by a converter-fed three-phase AC
machine is disclosed in DE 10 2004 060 206 B3. The converter used
has a field-oriented closed-loop control system. According to this
patent specification, a method for operating a converter-fed
compressor is specified with which the duration and intensity of
surge states are intended to be significantly reduced. With this
method, an actual operating state of the compressor is determined
from signal variables from the compressor drive converter and a
stored pump limit characteristic. By using signal variables from
the converter-fed three-phase machine, it can very quickly be
established whether an inadmissible operating state exists. The
variables torque-forming current component and the actual speed
value from the drive converter are used for this purpose. A pump
limit characteristic and a speed-dependent torque characteristic
are also required for this method.
SUMMARY OF THE INVENTION
The invention is now based on the object of specifying a method for
detecting a "rotating stall" fault in a converter-fed compressor,
with which signal variables from the drive converter are used.
According to the invention, this object is achieved by a method for
detecting a "rotating stall" fault in a compressor driven by a
converter-fed three-phase motor, with the steps of measuring
converter output currents and a signal proportional to a motor
speed, calculating from the measured converter output currents and
the measured speed-proportional signal an estimated torque value,
comparing the estimated torque value with a nominal torque value
determined from the measured speed-proportional signal and a
predetermined speed-proportional signal and, if the estimated
torque value is different from the nominal torque value, generating
a fault signal which indicates that a "rotating stall" fault has
occurred.
This invention is based on the knowledge that, with a converter-fed
compressor, a rotating stall leads to a dip in the armature current
of the converter-fed three-phase motor driving the compressor.
With the method according to the invention, a torque-forming
current component, which is equivalent to an estimated value of
torque, is calculated from measured converter output currents. A
setpoint for a torque-forming current component, which is
equivalent to a torque setpoint, is determined depending on a
measured speed-proportional signal and a predetermined
speed-proportional signal by means of a closed-loop speed control.
The estimated value of motor torque which is present in the
field-oriented closed-group control system is compared with a fixed
motor torque setpoint. If this estimated value deviates from the
fixed motor torque setpoint, a "rotating stall" fault exists.
Using drive variables which are already available enables
additional pressure sensors and/or vibration recorders to be
dispensed with.
Advantageous embodiments of the method according to the invention
can be seen from the dependent claims 2 to 7.
BRIEF DESCRIPTION OF THE DRAWING
To further explain the invention, reference is made to the drawing
in which an embodiment of a device for carrying out the method
according to the invention is shown schematically.
FIG. 1 shows a block circuit diagram of a converter-fed compressor
with a device for carrying out the method according to the
invention, and in
FIG. 2 a characteristic of a measured armature current in the event
of a "rotating stall" fault is shown in a diagram with respect to
time.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In FIG. 1, a device for carrying out the method according to the
invention is designated by 2, a load-side converter by 4, a
field-oriented closed-loop control system by 6, a three-phase motor
by 8, a unit for measuring a speed-proportional signal .omega. by
10, and a compressor by 12. The three-phase motor 8 is connected on
the stator side to outputs of the load-side converter 4, which is
also referred to as an inverter. The compressor 12 and the unit 10
for measuring a speed-proportional signal .omega. are mechanically
connected to the rotor of the three-phase motor 8. The load-side
converter 4 is part of a voltage source converter. On the DC side,
this load-side converter 4 is connected to a voltage source DC link
circuit to which a mains-side converter is also connected on the DC
side. Only the load-side converter 4 of this voltage source
converter is shown for reasons of clarity.
The field-oriented closed-group control system 6 has an actual
value computer 14 and a setpoint computer 16. The actual value
computer 14, very often also referred to as a flux computer, is
connected to measuring devices 18 and 20 for output currents
i.sub.S1, i.sub.S2 and i.sub.S3 and output voltages u.sub.S1,
u.sub.S2 and u.sub.S3 of the load-side converter 4. The actual
value computer 14, which has a current and a voltage model for
example, calculates orthogonal, field-oriented current components
.sub.mR and .sub.Sq and a flux orientation {circumflex over
(.epsilon.)} from these measured values i.sub.S1, i.sub.S2,
i.sub.S3 and u.sub.S1, u.sub.S2, u.sub.S3 and parameters of the
three-phase machine 8. If the actual value computer 14 has a
current model, then as well as the measured output currents
i.sub.S1, i.sub.S2 and i.sub.S3 of the load-side converter 4, this
current model also needs a speed-proportional signal .omega.. This
signal .omega. is likewise required in the setpoint computer 16 and
therefore this signal .omega. is shown with a dotted line in the
actual value computer 14. As the calculated actual values .sub.mR,
.sub.Sq and {circumflex over (.epsilon.)} are model variables,
these are shown with a "^" in each case.
The setpoint computer 16 has a speed control loop 22, a flux
control loop 24 and a torque control loop 26 on the one hand, and a
transformation device 28 on the other. The speed control loop 22
has a comparator 30 and a speed controller 32. The torque control
loop 26 likewise has a comparator 34 and a controller 36. This
torque control loop 26 is subordinate to the speed control loop 22.
From a predetermined setpoint .omega.* and an established
speed-proportional signal .omega., the comparator 30 forms a
control deviation which is controlled to zero by means of the speed
controller 32. A torque setpoint m* appears at the output of this
speed controller 32 and is compared by means of the comparator 34
with an estimated value of torque {circumflex over (m)}, which is
proportional to the established current component .sub.Sq. The
estimated value of torque {circumflex over (m)} is made to follow
the torque setpoint m* by means of the controller 36, at the output
of which a setpoint of an orthogonal current component .sub.Sq
appears. The orthogonal current component .sub.Sq is also referred
to as a torque-forming current component and is a current component
of the field-oriented "motor current" current vector. A flux
setpoint generator 38, the output side of which is connected to an
input of the comparator 40 of the flux control loop 24, is
connected upstream of the flux control loop 24. The calculated
estimated value of the orthogonal current component .sub.mR appears
at an inverting input of this comparator 40. This comparator is
connected on the output side to a flux controller 42, at the output
of which a setpoint of a second orthogonal current component
i.sup.*.sub.Sd appears. This second orthogonal current component
i.sup.*.sub.Sd is also referred to as a flux-forming current
component. These two current components i.sup.*.sub.Sd and
i.sup.*.sub.Sq are converted into orthogonal stator-oriented
current components i.sup.*.sub.S.alpha. and i.sup.*.sub.S.beta. by
means of a vector phase shifter 44 at the angle input of which a
calculated flux angle estimated value {circumflex over (.epsilon.)}
appears. Three current setpoints i.sup.*.sub.S1, i.sup.*.sub.S2 and
i.sup.*.sub.S3 of a three-phase current system are produced from
these orthogonal, stator-oriented current components
i.sup.*.sub.S.alpha. and i.sup.*.sub.S.beta. means of a coordinate
converter 46. These current setpoints i.sup.*.sub.S1,
i.sup.*.sub.S2 and i.sup.*.sub.S3 are fed phase-by-phase to a
comparator 48 in each case, which is connected on the output side
to a current controller 50 in each case. These comparators 48 are
also each connected on the input side to a measuring device 18.
The device 2 for carrying out the method according to the invention
processes the variables estimated value of torque {circumflex over
(m)} and torque setpoint m* of the drive consisting of load-side
converter 4 and three-phase motor 8 with compressor 12 in
accordance with the method according to the invention. The result
is a signal S.sub.RS which signals that the "rotating stall" fault
is occurring. In order to generate this signal S.sub.RS, the two
torque signals {circumflex over (m)} and m* are compared with one
another, the torque setpoint m* being a fixed value. Since this
torque setpoint m* is determined by means of a superimposed speed
control loop 22, this torque setpoint m* depends on the operating
point. If the calculated estimated value of torque {circumflex over
(m)} does not correspond to the fixed torque setpoint m*, then the
"rotating stall" fault is present.
A diagram of the characteristic of a measured armature current of
the three-phase machine 8 with coupled compressor 12 with respect
to time when a "rotating stall" fault occurs at a speed n=17000 rpm
is shown in FIG. 2. At time t.sub.RS1, the armature current dips
steeply and increases again at time t.sub.RS2. This armature
current has dipped as a result of the "rotating stall" fault.
In order to detect the occurrence of the "rotating stall" fault at
time t.sub.RS1 as soon after this time t.sub.RS1 as possible, the
estimated value of torque {circumflex over (m)}, which is
proportional to the torque-forming current component .sub.Sq of the
three-phase motor 8, is filtered, this filter having differential
elements. That is to say, when the "rotating stall" fault occurs at
time t.sub.RS1, the filtered estimated value of torque {circumflex
over (m)} changes its value in a step fashion while the fixed
torque setpoint m* remains constant. In order also to be able to
detect the "rotating stall" fault during a load change, a
established setpoint/actual value deviation of the torque, which
appears at the output of the comparator 34 of the torque control
loop 26 in the form of a control deviation, is compared with a
predetermined maximum value. If this maximum value is exceeded,
then the "rotating stall" fault is occurring during a load
change.
With a compressor which is driven by means of a converter-fed
three-phase motor 8, this method according to the invention enables
additional pressure sensors and/or vibration recorders to be
dispensed with, wherein the disadvantages of these additional
elements in the compressor 12 also no longer arise. In addition,
the "rotating stall" fault is detected reliably and synchronously
in time with the instant of its occurrence, enabling
countermeasures to be taken in good time.
These measures are: Reducing the speed: To do this, it is first
necessary to reduce the motor torque so that a counter torque of
the compressor 12 can act as a brake. The objective is to reduce
the mass flow in order to achieve a new stable operating point.
Increasing the speed: This requires initially increasing the motor
torque. The objective is to increase the mass flow and as a result
reach a stable operating point once more.
With the method according to the invention, already existing
signals of the converter-fed three-phase motor 8 are used to be
able to detect this "rotating stall" fault immediately after it has
occurred. This method according to the invention can be integrated
within the converter in the form of application software. By this
means, any compressor 12 which is driven by such a converter-fed
three-phase motor 8 can be monitored with regard to the "rotating
stall" fault without additional outlay.
* * * * *